Two cars collided about 9am in Engadine in southern Sydney on Sunday before the driver of one car allegedly began slashing at his passenger and good Samaritans who rushed to try and help the distressed woman.
Cronulla Sharks chairman Steve Mace said he came face-to-face with the knife-wielding man after the crash happened right in front of him on his way to his young son's junior football game.
He ran to the passenger's aid after hearing her screams but struggled to rip open the door to save her from the attack.
"I ... finally jammed it open and all of a sudden, I see him just slashing her," he said in a video posted by the Daily Telegraph.
"(He was) just cutting her neck, her breast ... in the sides, wherever he could go."
Mace described how another man, who was also trying to get the woman out of the car, ended up with a gash from his shoulder to his belly button before the knifeman left the car and made repeated attempts to attack the group.
"It was like a stand-off, which felt like an hour," Mace said.
"(He was going on about) it's a big conspiracy about the jab, and we're all getting followed, and we're all dead anyway."
The man allegedly tried to flee after police arrived and was tasered.
A male officer suffered a serious laceration to his left wrist, seemingly during the arrest.
All four injured people were treated by paramedics.
Mace said he escaped virtually unscathed - sustaining just a tiny cut to his finger.
Police will brief the media on the incident on Sunday afternoon.
A five-kilometre stretch of the Princes Highway was closed in both directions.
By Luke Costin
